Steve Smith says he will not be "stepping down" as Australian captain after he and his leadership group instructed Cameron Bancroft to tamper with the ball during the third Test against South Africa.

Smith has confessed he helped authorise the illegal practice of ball tampering on day three in Cape Town, while Bancroft admitted to the offence and was charged by match officials.

Players hatched the idea of cheating with yellow sticky tape, which they hoped would capture debris from the pitch and scuff one side of the ball in an attempt to get it to reverse swing, at lunch on Saturday (local time).

But Bancroft was caught doing it on the field by television cameras, and then attempted to hide the evidence by shoving the tape down his pants before he was questioned by umpires.

Smith admitted "the leadership group knew about it" but he would not name the other players involved in hatching the plan.

He said he had no intention to resign as Australian skipper.

"I won't be considering stepping down. I still think I'm the right person for the job," Smith told a media conference.

Bancroft has been charged with ball tampering by match referee Andy Pycroft but the heat is well and truly on Smith.

"Today was a big mistake on my behalf and on the leadership group's behalf as well," Smith said.

"I take responsibility as the captain. I need to take control of the ship.

"I'm incredibly sorry for trying to bring the game into disrepute the way we did.

"This is certainly something I'm not proud of and something that I can hope to learn from and come back strong from.

"My integrity, the team's integrity, the leadership group's integrity has come into question."

Aussies 'deeply' regret ball tampering

Cricket Australia boss James Sutherland said the incident was "a very sad day for Australian cricket" but he would not be making any rash decisions on Smith's future.

He said CA's head of integrity Iain Roy was travelling to South Africa to lead an investigation into the incident.

"Steve Smith is currently the captain of the Australian team," Mr Sutherland said.

"We're working through a process … once we get a clearer picture of the facts and understand things and once Iain submits his report we'll be able to make further comment."

Smith said in the post-day media conference that he was disappointed in the actions of his team.

"We spoke about it at lunch and I'm not proud of what's happened. It's not within the spirit of the game," he said.

"We spoke about it and thought it was a possible way to get an advantage … poor choice and, yeah, we're deeply regrettable."

The tampering and hiding of the tape was replayed over and over in slow motion and close up, on the big screen at Newlands and on television. Bancroft then confessed.

"I saw an opportunity to potentially use some tape and get some granules from the rough patches of the wicket and try to change the ball condition," Bancroft said.

"It didn't work. Once I was sighted on the [stadium] screen I panicked quite a lot, and that resulted in me shoving it [the tape] down my trousers."

The confessions by Smith and Bancroft at the post-day media conference provided the most shocking moment in a series that has contained a multitude of contentious incidents and off-field drama. None as jaw-dropping as this, though.

It has not been revealed if Smith and other players were facing charges of bringing the game into disrepute.

They can be charged under the International Cricket Council code of conduct and bans could be handed out.

'Wrong place at the wrong time'

Smith and Bancroft revealed a conspiracy in the Australian dressing room where senior players roped in Bancroft, who then got caught by television cameras.

Bancroft said he was "in the wrong place at the wrong time" when he got involved.

"I was in the vicinity of the area when the leadership group were discussing it and look, I'll be honest with you, I was obviously nervous about it because with hundreds of cameras around there's always a risk, isn't it?" he said.

Smith insisted coaches were not involved in the plan in Cape Town and had no knowledge of it, and he declined to name the other players involved.

The team's "leadership group" has previously included vice-captain David Warner and bowlers Nathan Lyon, Mitchell Starc, and Josh Hazlewood.

"I'm not naming names," Smith said.

He also said this was the first time tampering happened on his watch as captain, denying that Australia's big victory in the opening Test in Durban, where fast bowler Starc got the ball to reverse swing with deadly effect, was also aided by tampering.

Using a foreign object to rough up or change the condition of one side of the ball can help it swing in the air or do other unpredictable things, making it tougher for batsmen to face.

The use of foreign objects to tamper with the ball is strictly prohibited in cricket.

The incident cast light on previous Australia successes and other moments in this series.

Warner came under scrutiny in the second test in Port Elizabeth for strapping he wore on one of his hands, with suggestions it could change the condition of the ball when he rubbed it with that hand.

"You can ask questions as much as you like but I can promise you that this is the first time that this has happened," Smith said.

"I've made it clear that we're regrettable and we'll move on from this and hopefully we'll learn something from it. I'm embarrassed and I know the boys in the shed are embarrassed as well."

Smith said, "if we weren't caught, I'd still feel incredibly bad about it".

Also subject to scrutiny is how far the Australians went to try and cover up the tampering.

There was movement of players, including Smith, on and off the field in the immediate aftermath of Bancroft's actions being caught on cameras.

'This is cheating'

The cricket media have condemned the actions of Smith and the Australian team, with many arguing he has to step down as captain.

Cricket analyst Catherine McGregor said Smith had no choice but to resign following his admission.

"It's just an appalling and deliberate systematic attempt to undermine the rules and laws of the game," McGregor told the ABC.

"I think the captain's position's untenable. There's no euphemism left for this, this is cheating."

Journalist Richard Hinds believed there was grounds for offering sympathy to Bancroft, who he claimed was "thrown under the bus" by Smith and his senior teammates.

"He's got a decision to make," Hinds said on Offsiders.

"Put yourself in his shoes and he says, 'look, I'm going to stand up for myself here and [be] uncomfortable with it and I'll say no'.

"Or is he thinking I want to play the fourth Test and continue to play for Australia?"